(1) Field of the Invention
The present invention relates to telephone systems and more particularly to a tone ringer for use in a telephone subscribers subset.
(2) Description of the Prior Art
Traditionally telephone subset ringers have been of the electromechanical type which includes an electromagnet operated in response to ringing signals, to cause a clapper or hammer type of mechanism to strike a bell or gong. Such electromechanical units are large in size and consequently difficult to include in present day telephone subsets. To overcome this problem electronic tone ringers have been developed.
Examples of the current state of the art of electronic tone ringers include U.S. Pat. No. 3,808,379 issued to P. U. Lind on Apr. 30, 1974 and U.S. Pat. No. 3,867,585 issued to R. A. Morstadt on Feb. 18, 1975. However, both of these circuits use a standard telephone receiver which is efficient as a tone ringer output device. Both of these circuits also use resistor-capacitor controlled oscillators to determine the frequency of the tone output. Thus the accuracy and consistency of frequency control depends on the accuracy of the resistor-capacitor time constant and the electrical properties of the semi-conductor devices used in the oscillators.
Accordingly, it is the object of the present invention to provide an electronic tone ringer using a high efficiency transducer and consistent frequency control independent of the accuracy of a resistor-capacitor time constant and the electrical properties of semi-conductors. A further object is to provide reliable performance under low voltage conditions.